Adapter Specification
The Compaq VAX™-SCSI Wide Ultra SCSI Host is based on the LSI
53C875 SCSI controller chip. This chip includes the following:
Onboard RISC processor
Internal 512Byte FIFO
Internal 4Kbyte Script RAM
One interrupt per I/O scripts
IntraServer’s SCSI script implementation on the Symbios (LSI Logic)
53C875 SCSI processor offloads the CPU to deliver higher efficiency and
lower CPU utlization. All low level SCSI functions are completed by
SCRIPTS, which only interrupt the host when an I/O is complete. This
allows the SCSI interface to perform at a higher I/O rate than previous
implementations, which were limited by the processor’s ability to service
frequent interrupts.
Adapters designed for systems with a CDAL bus (Compaq adapters versions
DS-KZCCA-AB, -BB, -CB and -DB) interface directly to the CPU on the
CDAL bus, allowing for maximum I/O bandwidth possible for these systems.
Compaq’s DS-KZMCA-AB adapter (currently under development)
implements the XMI interface, and is intended to be used in XMI based
The high performance PCI SCSI core is interfaced to the system bus (CDAL
or XMI) by use of a Field Programmable Gate Array. The FPGA provides
arbitration for the PCI devices (SCSI and Ethernet are available options),
interrupt controll and data path.
Required Software
IntraServer’s PKW driver, a high performance Wide Ultra SCSI driver is
used as the port driver for the VAX-SCSI implementation. PKW is a port of
IntraServer’s PKWDRIVER which has been fully qualified by digital, and is
now part of the OpenVMS/Alpha distribution (V7.1-2 and V7.2). PKW
interfaces with the high performance scripts on the 53C875 to maximize
SCSI data throughput while minimizing CPU overhead.
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